Many people are at increased risk of injury or death as a result of a chronic health condition or complications resulting from acute illness, disability, or advancing age. Many other people suffer from chronic, or at least sustained, conditions that require long term treatment. Other people, such as soldiers, police, fire fighters, rescue workers, etc., work under hazardous and life-threatening conditions. In many instances, detecting a fall of these individuals is necessary to render aid when needed to prevent further health issues that could result from a fall.
Monitoring altitude change of a wearable fall detecting apparatus can detect a fall of a user. Usually, the altitude of a fall detecting apparatus worn at the neck of the user will change about 60 cm when a fall occurs. Therefore, whether a fall occurs or not can be detected by checking the altitude change of the fall detecting apparatus. To obtain the altitude change of the fall detecting apparatus, a pressure sensor is a good candidate sensor that can measure atmosphere pressure, which can be converted into an altitude value.
When the altitude value is taken into consideration for detecting a fall, it would be better to have a pressure sensor that can obtain an altitude value with a resolution of about 10 cm, allowing a fall to be detected correctly without a false dismissal or a false alarm. However, a pressure sensor cannot fulfill the resolution requirement of 10 cm when the pressure sensor's orientation varies.
FIG. 1 illustrates a schematic diagram of a pressure sensor SCP1000-D01 produced by VTI Technologies, and FIG. 1 (b) illustrates measured altitude values vs real altitude values when the orientation of the pressure sensor varies. The dashed line with triangles corresponds to the situation when the pressure sensor's surface with the text “D01” is vertical to the ground; the solid line with squares corresponds to the situation when the pressure sensor's surface with the text “D01” faces upward; and the dash-dot line with diamonds corresponds to the situation when the pressure sensor's surface with the text “D01” faces downward.
Referring to FIG. 1 (b), the pressure sensor may obtain an altitude variation value with an error of 50 cm if the pressure sensor's surface with the text “D01” turns from upward to downward. In fall detection applications, an altitude value with an error of 50 cm cannot be accepted because it will generate a false dismissal or a false alarm. The reason for an error of the altitude value is that the atmosphere pressure is measured by detecting the deformation, in response to the atmosphere pressure, of a pressure sensing element comprised in the pressure sensor, and the weight of the pressure sensing element affects the deformation of the pressure sensing element when the pressure sensor's orientation varies. In addition, a protective gel is provided on the pressure sensing element to protect the pressure sensing element from moisture, and the weight of the protective gel also affects the deformation of the pressure sensing element.